I've studied this process quite a bit. Appetite for destruction was a very creative stereo spectrum layout.
Mike Clink was really experimenting at this time more than anything. It just so happened with the sound of the guitars, it works incredibly well. (Izzy on the L / Slash on the R and solos in the C position).
In your situation you want the guitars to be distinguishable. If not your just making it sound like a wall of mush.
Use different guitars, different /Amps/Amp Sims. Tame the harsh frequency's. Don't be afraid to lay heavy on one side (panned hard Right) you can correct shift in the mix but I've heard great sounds from Heavy guitars on one side in many good songs.
Remember Izzy and Slash both used different guitars and different amps.
The key here, is stacking, keeping phase relation and making them sound a little bit different from each other. Using the same guitar/amp on 6 guitar tracks will get you exactly what you ask for...Indistinguishable mush.